To study shark behavior, researchers in Hawaii are mounting video cameras – called “Crittercams” – on reef shark fins. Scientists are looking for new information about how the predators pass the time. Researchers have made use of satellite tags on sharks and many other species for years. However, improvements in the technology in use have made possible a detailed three-dimensional reconstruction of how the sharks swim, as well as an analysis of how much energy they expend while swimming. Investigations of animal habitats and behavior are critical to understanding the animals’ ecology, in order to make informed decisions about animal conservation efforts.
Shark foraging ecology and feeding until now has been challenging, since predation events are witnessed only rarely. Most information comes from either anecdotal observations or stomach content analysis. Analysis of stomach contents is useful, but may not be helpful in estimating the relative importance of a particular prey type, or in identifying the habitat where the shark was feeding, making definition of critical habitats difficult.
The technology currently in use for the study of shark behavior includes magnetometers and accelerometers, and a video camera, called a “crittercam” – something like the recorders in use on police cars that make the Cops television show possible. Magnetometers and accelerometers enable the recording of fine details about a shark’s position, including the shark’s acceleration and the surrounding magnetic field. Other instruments take note of water temperature and depth. The instrument package has been compared with the “blackbox” that records flight data on an airplane.
Carl Meyer is one of the researchers on the project. He is interested in answering questions about the top predators such as: movement patterns and habitat use; what sort of food they eat; how physical oceanography affects top predator movements; and the ecological impact of shark ecotourism. Other questions he is approaching include the navigational abilities of the sharks – their magnetic sense, and their cognitive mapping.
On the National Geographic Website, numerous videos – called “crittercams” – are available, made with equipment placed on all sorts of wild animals for the purpose of learning what they like to do when they don’t know that we’re watching. The videos include hunting, mating, eating, and lazing-around-the-Savannah behavior.
One video from the shark study showed a sandbar shark beginning the day at 300 feet below the surface, then swimming upward as the day progressed, eventually joining a school of other sandbar sharks, scalloped hammerheads, and oceanic blacktips. The researchers believe the schooling sharks were seeking safety in numbers from tiger sharks – voracious predators up to 12 feet in length, which, in addition to being the largest costal shark in Hawaii, make up almost half of their diet from other sharks. Sharks like hammerheads, sandbars, and oceanic blacktips get together in schools, to escape being eaten by the tiger sharks.
Meyer and the other researchers reported their results on Friday at an oceanography conference in Hawaii. Future plans include retrieving their instruments and performing data analysis. They’re also planning to get their equipment onto bluntnose sixgill sharks—about which little is known, since they live over the outer continental and insular shelves, resting along the bottom during the day at depths of 6,500 feet, and swimming closer to the surface or into shallow waters to feed at night.
Scientists use the crittercam to study shark behavior carefully for a number of reasons. Foremost among these is the fact that sharks are “keystone” species – that is, species without which the food web of an entire ecosystem would collapse. Additionally, sharks are subject to intense fishing pressure because of a high demand for shark fins and cartilage, seen as medicinal in some countries, and also treated as food. Sharks travel long distances, across entire oceans and in different national waters, thus they are susceptible to unregulated fishing by multiple nations. As a consequence, shark populations have plunged below 30 percent of their numbers 20 years ago. Their slow reproductive rate and the unregulated hunting of the sharks have caused concern about the health of shark populations, inviting an important dialogue about effective conservation and management, and creating a need for the best information possible on shark behavior.
By Laura Prendergast